1. Technical Field
The present invention relates to a method for up-shifting of an automatic or semiautomatic gearbox which is connected to an engine equipped with an auxiliary engine brake, which method comprises determining an expected value of the velocity derivative of said engine during said gear-shifting.
The invention also relates to a device for up shifting of an automatic or semi-automatic gearbox which is connected to an engine equipped with an auxiliary engine brake, comprising a control unit for initiating gear-shifting and for storing an expected value of the velocity derivative of said engine during said gear-shifting.
2. State of the Art
Commercial vehicles, such as trucks and buses, are normally equipped with an engine brake function to spare the wheel brakes of the vehicle during braking. In this context, it is previously known to provide an engine braking effect in an internal combustion engine by means of arranging a choke organ, for example in the form of a valve, in the exhaust system of the vehicle. In this manner, a certain portion of the work during the exhaust stroke of the piston can be used to increase the braking effect.
Another kind of engine brake is a so-called compression brake, which operates by means of choking one or more of the exhaust valves of the engine so that the air which been compressed during the compression stroke of the engine in the combustion chamber is partially allowed to flow out into the exhaust system. This means that part of the compression work carried out during the compression stroke is not re-used during the expansion stroke of the engine, which is utilized for a braking effect on the crank shaft.
In a known compression brake the exhaust valves are controlled in such a manner that the camshaft of the engine is given a profile which is shaped with at least one extra ridge in order to achieve an opening of the exhaust valves to generate braking effect. Also, the valves are shaped with a small play, the size of which is chosen (together with the dimensions of the extra ridge), so that the extra ridge does not effect the valves during normal engine operation. For this purpose, the extra ridge has a lifting height which is very small compared to the regular exhaust ridge. In order to make the extra ridge operable during engine braking, i.e. so that the exhaust valves can be opened when engine braking, each rocker arm is shaped with a device in the form of a displaceable piston which is effected by oil to be placed in a protruding position. This causes the valve play to be eliminated, and the lifting height of the extra ridge then becomes sufficient to open the exhaust valves.
Apart from utilizing an engine braking device for braking the vehicle as such, i.e. as a complement to the wheel-brakes of the engine, there is also a desire to use an engine braking device, such as for example a compression brake, during shifting of the gearbox of the vehicle. It can here be seen that commercial vehicles such as trucks and buses are more and more frequently equipped with automatic or semiautomatic gearboxes. Such gearboxes can be likened to conventional manual gearboxes, with the difference that the gear-shifting is carried out by means of maneuvering devices instead of manually by driver. The appended FIG. 1 shows the principal phases in connection with an up-shifting (i.e. to a higher gear) in such a gearbox. FIG. 1 shows a comparison between engine torque and engine speed relative to time in a given type of engine.
As can be seen in FIG. 1, phase “a” shows a normal driving condition before a gearshift is initiated. Phase “b” shows the removal of the engine torque as soon as the decision has been made to carry an up-shift. Phase “c” shows the release of a claw coupling in order to decouple the gearbox from the engine. Phase “d” shows a decrease of the engine speed in order to match the engine speed to the gear ratio that is to be chosen. As soon as the engine speed has decreased sufficiently, the new gear can be engaged. Thus, phase “e” shows the engagement of the new claw coupling. Phase “f” shows the restoring of the torque, and phase “g” shows a normal driving condition after the gear-shifting has taken place.
In order to reduce the loss of driving energy of the vehicle during an up-shift, it is advantageous if the engine speed can be matched to the new gear ratio as rapidly as possible. From document SE-C-502154 it is known to selectively use an exhaust brake during up-shift when certain operational parameters are achieved in order to thus obtain a rapid decrease of the engine speed during the gear-shifting process. In this way the wear on the exhaust brake system allegedly decreases, since the use of the exhaust brake is only carried out during a small portion of the total amount of up-shifts.
From Swedish patent application number 9804439-9, an arrangement is previously known for engine braking in connection to an internal combustion engine. This arrangement is adapted for engine braking by means of decreasing the engine speed when shifting gears, and for this purpose comprises a special device which is sensitive to a signal which is generated as an answer to a need to obtain a gearshift and in order to obtain an absorption of a valve play in a rocker arm.
When shifting gears in an engine, there is generally a desire for the time for the power cut-off, PCOT of the engine, to be made as small as possible. According to prior art, there is during gear-shifting generated first a signal that indicates that the gear-shifting is going to take place. After initiating the gear-shift and removing the engine torque, the rpm of the engine will successively decrease, mainly due to friction forces in the moving parts of the engine. Finally, a lower rpm will have been reached at which the gear-shifting can be completed. In order to additionally shorten the power cut-off time during gear-shifting engine, braking can also take place, as has been mentioned above.
A further desire in connection to gear-shifting is that the gear-shifting process should always take place while maintaining optimal parameters of the engine and the rest of the vehicle. Carrying out a gearshift can be affected by a number of parameters, such as the slope of the road, the air and rolling resistance of the vehicle etc, and there are naturally demands to, as far as possible, avoid incomplete gear-shifting and other main functions. If, for example, the power cut-off time is too long, it can be difficult to carry out gearshifts at all, which causes the engine to stop. Another difficulty which can arise is that different engine combinations and different vehicles can exhibit slight variations regarding performance and function including the engine brake function. This means that, for example, gear-shifting can be carried out during somewhat different conditions on different vehicles. There is thus a need to compensate for such individual variations that can influence the gear-shifting.